Copolymers of ethylene and acrylic esters are crosslinked by converting some of the ester groups to ester or amide groups which contain unsaturation and then sulfur or peroxide curing the resulting polymers.
Crosslinking (also sometimes termed vulcanization or curing) of polymers yields products which often have improved properties for their intended uses. This is particularly true when the polymer is an elastomer, and curing of elastomers is very commonly done, for instance using sulfur or peroxide curing. For sulfur cures, generally speaking the polymer contains olefinic unsaturation, while for peroxide curing the presence of olefinic unsaturation is often preferable, see for instance H. Mark, et al., Ed., Encyclopedia of Polymer Science and Engineering, Vol. 17, McGraw-Hill Book Co., New York, 1989, p. 666-698.
However, some types of elastomers do not contain olefinic unsaturation, and so are not generally sulfur cured, and/or cured by peroxides with some difficulty. These elastomers are cured using other curing systems. For example, elastomeric ethylene/acrylic copolymers may be crosslinked by the use of primary diamines, which form crosslinks, see for instance H. Mark, et al., Ed., Encyclopedia of Polymer Science and Engineering, Vol. 1, McGraw-Hill Book Co., New York, 1985, p. 325-334. In order to aid in such crosslinking to more readily form crosslinks and/or form more stable crosslinks curesite monomers, such as carboxylic acids or half acid esters may be copolymerized into the polymer, see for instance U.S. Pat. Nos. 3,883,472 and 3,904,588. However, it is often desirable to crosslink such polymers using sulfur or peroxide cures, because such cures are already in use in many factories for a wide variety of common elastomers, and/or the curing agents are less expensive and/or less toxic. In order to make such types of polymers peroxide and/or sulfur curable, it is desirable to introduce into them olefinic unsaturation containing groups. These groups should be introduced in such a way so as not to harm the basic polymer properties, so that the polymers may be readily and/or economically cured, and/or the resulting crosslinks are stable (so as to give good vulcanizate properties).
Japanese Patent Application 62-121746 describes the esterification of a polymer made from ethylene, an acrylic ester and maleic anhydride and/or a maleic half acid ester which is xe2x80x9cmodifiedxe2x80x9d with an olefinically unsaturated amine or alcohol, and then cured using a sulfur or peroxide cure. No mention is made of polymers containing only ethylene and acrylic ester repeat units.
German Patent Application 3,715,027 A1 describes various copolymers of ethylene and acrylic acids and/or esters, and optionally other monomers such as maleic anhydride, their reaction with olefinic alcohols, including those with polyunsaturation, and their subsequent crosslinking by oxidation, e.g., reaction with air, often in the presence of an oxidation catalyst. The polymers are useful as thermosetting melt adhesives. No mention is made of sulfur or peroxide curing.
U.S. Pat. No. 5,736,616 is similar to German Patent Application 3,715,027, in that a polymer containing pendant unsaturation is used as an oxygen scavenger (react with oxygen). The polymer is made by polymerizing ethylene and acrylic esters and/or acids and then esterifying or transesterifying the resulting polymer with an unsaturated alcohol. No mention is made of curing such a polymer using a sulfur or peroxide cure.
U.S. Pat. No. 5,093,429 describes the preparation of a polymer containing olefinic unsaturation by direct copolymerization of ethylene, an acrylic ester, and a copolymerizable monomer containing unsaturation which survives the polymerization (for example has a copolymerizable double bond and a double bond which is unreactive in the polymerization), or by copolymerization of ethylene, and acrylic ester, and another copolymerizable monomer which may then be reacted with an unsaturated alcohol or amine to attach such unsaturation to the polymer. The polymer containing unsaturation may then be crosslinked using a sulfur or peroxide curing system. No mention is made of using the acrylic ester as a site to attach the olefinic unsaturation.
In some instances the crosslinks that result from curesite monomers present in some of the above references are not as stable as desired because linkages between the crosslinkable groups (e.g., olefinic unsaturation) are not as stable as desired (for example U.S. Pat. No. 4,399,263 mentions that at temperatures above 160xc2x0 C. ethylene/alkyl acrylate/maleic acid ester polymers form anhydride moieties by internal reaction at the acid-ester curesite). The crosslinks may not be sufficiently stable because the curesite monomers and/or polymer-modifying reagents, which attach curable functionalities onto the polymer, introduce groups into the composition which catalyze unwanted reactions.
This invention concerns a process for crosslinking a polymer, comprising:
(a) transesterifying or amidating a first polymer consisting essentially of about 10 or more mole percent of ethylene, about 10 or more mole percent of 
and up to about 10 mole percent, total, of one or more hydrocarbon olefins, with an alcohol or a primary amine which contains one or more olefinic bonds, to form a second polymer having side chains with said olefinic bonds; and
(b) crosslinking said second polymer using a sulfur or peroxide cure system;
and wherein:
R1 is methyl or hydrogen; and
R2 is hydrocarbyl or substituted hydrocarbyl.
Also disclosed herein is a composition comprising:
(a) a polymer made by transesterifying or amidating a first polymer consisting essentially of about 10 or more mole percent of ethylene, about 10 or more mole percent of 
and up to about 10 mole percent, total, of one or more hydrocarbon olefins, with an alcohol or a primary amine which contains one or more olefinic bonds, to form a second polymer having side chains with said olefinic bonds; and
(b) a sulfur or peroxide cure system;
and wherein:
R1 is methyl or hydrogen; and
R2 is hydrocarbyl or substituted hydrocarbyl.
Another composition disclosed herein comprises:
(a) a polymer consisting essentially of about 10 or more mole percent of ethylene, about 10 or more mole percent of 
and up to about 10 mole percent, total, of one or more hydrocarbon olefins; and
(b) a sulfur or peroxide cure system;
and wherein:
R1 is methyl or hydrogen; and
R2 is hydrocarbyl or substituted hydrocarbyl, provided that at least 0.5 mole percent of R2 contains olefinic unsaturation.